Replies to This Discussion

Permalink Reply by Gecko on March 8, 2010 at 4:45pm

There are ways of measuring for any crankset before even mounting it, but it's a little hard to explain on the internets. I could take some pics and do a little tutorial for you if you want.

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Permalink Reply by mfa cycle factory on March 8, 2010 at 6:50pm

please post up a tut... fine brew for you to splat your tonsils with is on me.

thanx



El Gecko said:

There are ways of measuring for any crankset before even mounting it, but it's a little hard to explain on the internets. I could take some pics and do a little tutorial for you if you want.

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Permalink Reply by Primitive Don on March 9, 2010 at 5:05am

I would become familiar with Sheldon Brown's Bottom Bracket Size Database. It will give you a good idea of what length spindle is intended for many cranksets, and has a table showing the lengths of Japanese spindles by code (3H = 113mm etc.).

If you are converting bikes to SS/FG, then there is a often a desire to use a spindle/BB that is shorter than for a road double in order to get a better chainline, and that's when you start running into the chain stays. In that case, you'd need to use the next size larger spindle/BB to clear the stays. Also, some spindles are asymmetrical, meaning one side sticks out further than the other, so you can sometimes flip a spindle end-for-end to improve the chainline or chainstay clearance. Hope this helps.

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Permalink Reply by mfa cycle factory on March 9, 2010 at 5:09pm

thanks for the follow up.

I'm fimiliar with SB's overview of BB.
The problem is I run into cranksets like
Silstar(made by SR),and enven though they
are kick ass cranksets,there isn't a lot of data on them,and SB does not have any info on them either.

however,the chart does come in handy.

What I've been doing lately is using a happy medium system. JiS spindles are shorter in
length and ISOs are longer,so I'll take a spindle that is about 110mm and pretty much eye-gauge it from there,and flip flop the spindle if needed.....

but I would still like to have a proper mathematical system with my BB/crankset installations.

thanks.....,now I'm going to have to post up
some helpful bike building info for others since you are going out of your way to create a tut.....

you def get major cool points for that.

Primitive Don said:

I would become familiar with Sheldon Brown's Bottom Bracket Size Database. It will give you a good idea of what length spindle is intended for many cranksets, and has a table showing the lengths of Japanese spindles by code (3H = 113mm etc.). If you are converting bikes to SS/FG, then there is a often a desire to use a spindle/BB that is shorter than for a road double in order to get a better chainline, and that's when you start running into the chain stays. In that case, you'd need to use the next size larger spindle/BB to clear the stays. Also, some spindles are asymmetrical, meaning one side sticks out further than the other, so you can sometimes flip a spindle end-for-end to improve the chainline or chainstay clearance. Hope this helps.

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Permalink Reply by Gecko on March 9, 2010 at 4:48pm

Good call Don, I was going to suggest that as well. The Square Taper BB Interchangeability is a good one too.

As for the tutorial, I took the pics tonight but I left the program I'm going to build it in at work. I should have something up by tomorrow evening.

Primitive Don said:

I would become familiar with Sheldon Brown's Bottom Bracket Size Database. It will give you a good idea of what length spindle is intended for many cranksets, and has a table showing the lengths of Japanese spindles by code (3H = 113mm etc.).

If you are converting bikes to SS/FG, then there is a often a desire to use a spindle/BB that is shorter than for a road double in order to get a better chainline, and that's when you start running into the chain stays. In that case, you'd need to use the next size larger spindle/BB to clear the stays. Also, some spindles are asymmetrical, meaning one side sticks out further than the other, so you can sometimes flip a spindle end-for-end to improve the chainline or chainstay clearance. Hope this helps.

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Permalink Reply by Michael Perz on March 9, 2010 at 5:23pm

For whatever it's worth, Phil Wood makes BBs that allow for slight chainline adjustment.

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Permalink Reply by Primitive Don on March 10, 2010 at 5:31am

It is a shame that there is no data listed for SR cranks, since they made so many cranks. But whaddygonna do? Even if you have all the data, there are still other factors, such as whether or not the cranks have ramps that might run into the stays, the angle of the chainstays, etc. Plus sometimes you get conflicting data from different sources. I ran into that finding replacement cranks for a 90s Trek mountain bike. There's always going to be a certain amount of trial and error substituting parts, but that's part of the fun.

I may lose some cool points here, but some builder friends have me hooked on cartridge BBs. I used a 110 on my last SS conversion of a Sanwa road bike that formerly had a Shimano 600 double crankset, and everything lines up well.

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Permalink Reply by Gecko on March 11, 2010 at 5:39pm

Well, here goes. I was going to make a nice instructional video but unfortunately I really don't have the time.

ALL MEASUREMENTS IN MILLIMETERS

DISCLAIMER: This isn't an exact science, it's just one way to do it, and there is a certain margin of error. This is the way I use, and it gets close enough for me.

First you'll need the chainline from the rear hub after the wheel is mounted. Basically you need to know the exact axle spacing and divide in half. Then you'll measure from the outermost drive side locknut to the center of the teeth on the cog/freewheel, and subtract that from half the axle length. Then you'll need to know how far the outside of the spindle interface (where the crank bolt presses against when tightened) is from the center of the teeth on the chainring. The easiest way to do this is to find a small, flexible ruler, bend or cut it and push it in the spindle hole from the frame side of the crank. Then line the outside (only the square part, not the removal threads) up with the zero on the ruler, and lay a straight edge along the inside of the chainring, and take the measurement where the straight edge meets the ruler. Then take the thickness of the chainring and divide by two to find the center, then subtract that from the previous measurement with the straight edge. If you've done it right, you should be able to add the chainring-to-interface measurement to the chainline measurement, subtract 1.5mm on either side for excess taper, and get a reasonably close spindle length.

Example:
Say I had a 120mm axle on my hub and a 17mm locknut-to-cog measurement. (Cog already mounted to hub, hub mounted in frame.)
120mm / 2 = 60mm (half axle length)
60mm - 17mm = 43mm
So I have a 43mm chainline from my rear hub.

The chainring-to-interface measurement is 16mm. (Chainring already mounted in desired position on crank.)
43mm + 16mm = 59mm
59mm X 2 = 118mm
total excess taper: 1.5mm X 2 = 3mm
118mm - 3mm = 115mm

So I would need a 115mm spindle, standard size for a road double crankset.

To measure for chainring clearance, you'll need to measure the radius of your chainring (including teeth). Then measure that amount from the center of the bb shell back toward the back of the bike, making sure to keep the ruler in the center of the frame. Once you find where the radius is on the chainstays, measure the outside width of the chainstays at that point. Then divide by two. If that number is bigger than your chainline number (43mm for example), you'll need to decrease the size of the chainring until it fits, or get a longer bb spindle.

You can do the same thing with the crank arm. First find out the crank arm length and substitute it for chainring radius above ^. Then measure from the center of the chainring to the inside edge of the crank arm end, add that measurement to the chainline, and substitute that measurement for the chainline above ^.

If you run into crank arm or chainring clearance issues with the cranks/bb already installed, just measure the distance from the inside of the pedal end of the crank arm to the outside of the chainstay and add that much plus at least 3mm (for clearance) to each side of the spindle length.

Example:
Say I had a 107mm spindle and my crank arms were inside the chainstays by 1mm.
1mm + 3mm = 4mm
4mm X 2 = 8mm
107mm + 8mm = 115mm spindle
Then you'd have to respace your rear hub 4mm farther to the drive side, or put a 4mm spacer on your cog/freewheel.

It's also a good idea to measure the offset of the left and right side crank arms separately to check if the crankset needs an offset spindle. To do this, just place the crank arm, frame side down, on a flat surface, and push on the bb end so it's flat and the pedal end is in the air. Then measure from the flat surface (table, etc.) to the bottom of the crank arm at the pedal end. If both sides are within a few mm, you should be fine with a standard spindle. If I remember right, if they are more than 5mm apart, you'll need an offset spindle, but I'm not positive.

By the way, this was written with cartridge bottom brackets in mind, but it applies to adjustables just as well.

Let me know if any of this doesn't make sense and I'll try to explain further.

Also, you should be careful interchanging JIS and ISO spindles/cranks. If you use JIS cranks on ISO spindles, you could tighten too far and expand the taper so that the tightening bolt bottoms out on the spindle.

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Permalink Reply by mfa cycle factory on March 11, 2010 at 6:25pm

Makes sense and similar to the data SB has on his site.. thanks for this.....It will come in handy.

I very rarely interchange bottom brackets, even though its a legal method as far as functionality goes. I do make sure that there is at least 1/8th of an inch thread sitting inside of the crank square so that the
bottom bracket nut will tighten against the crank and not against itself.

again, thanks for the data....it will come in handy.....

El Gecko said:

Well, here goes. I was going to make a nice instructional video but unfortunately I really don't have the time.

ALL MEASUREMENTS IN MILLIMETERS

DISCLAIMER: This isn't an exact science, it's just one way to do it, and there is a certain margin of error. This is the way I use, and it gets close enough for me.

First you'll need the chainline from the rear hub after the wheel is mounted. Basically you need to know the exact axle spacing and divide in half. Then you'll measure from the outermost drive side locknut to the center of the teeth on the cog/freewheel, and subtract that from half the axle length. Then you'll need to know how far the outside of the spindle interface (where the crank bolt presses against when tightened) is from the center of the teeth on the chainring. The easiest way to do this is to find a small, flexible ruler, bend or cut it and push it in the spindle hole from the frame side of the crank. Then line the outside (only the square part, not the removal threads) up with the zero on the ruler, and lay a straight edge along the inside of the chainring, and take the measurement where the straight edge meets the ruler. Then take the thickness of the chainring and divide by two to find the center, then subtract that from the previous measurement with the straight edge. If you've done it right, you should be able to add the chainring-to-interface measurement to the chainline measurement, subtract 1.5mm on either side for excess taper, and get a reasonably close spindle length.

Example:
Say I had a 120mm axle on my hub and a 17mm locknut-to-cog measurement. (Cog already mounted to hub, hub mounted in frame.)
120mm / 2 = 60mm (half axle length)
60mm - 17mm = 43mm
So I have a 43mm chainline from my rear hub.

The chainring-to-interface measurement is 16mm. (Chainring already mounted in desired position on crank.)
43mm + 16mm = 59mm
59mm X 2 = 118mm
total excess taper: 1.5mm X 2 = 3mm
118mm - 3mm = 115mm

So I would need a 115mm spindle, standard size for a road double crankset.

To measure for chainring clearance, you'll need to measure the radius of your chainring (including teeth). Then measure that amount from the center of the bb shell back toward the back of the bike, making sure to keep the ruler in the center of the frame. Once you find where the radius is on the chainstays, measure the outside width of the chainstays at that point. Then divide by two. If that number is bigger than your chainline number (43mm for example), you'll need to decrease the size of the chainring until it fits, or get a longer bb spindle.

You can do the same thing with the crank arm. First find out the crank arm length and substitute it for chainring radius above ^. Then measure from the center of the chainring to the inside edge of the crank arm end, add that measurement to the chainline, and substitute that measurement for the chainline above ^.

If you run into crank arm or chainring clearance issues with the cranks/bb already installed, just measure the distance from the inside of the pedal end of the crank arm to the outside of the chainstay and add that much plus at least 3mm (for clearance) to each side of the spindle length.

Example:
Say I had a 107mm spindle and my crank arms were inside the chainstays by 1mm.
1mm + 3mm = 4mm
4mm X 2 = 8mm
107mm + 8mm = 115mm spindle
Then you'd have to respace your rear hub 4mm farther to the drive side, or put a 4mm spacer on your cog/freewheel.

It's also a good idea to measure the offset of the left and right side crank arms separately to check if the crankset needs an offset spindle. To do this, just place the crank arm, frame side down, on a flat surface, and push on the bb end so it's flat and the pedal end is in the air. Then measure from the flat surface (table, etc.) to the bottom of the crank arm at the pedal end. If both sides are within a few mm, you should be fine with a standard spindle. If I remember right, if they are more than 5mm apart, you'll need an offset spindle, but I'm not positive.

By the way, this was written with cartridge bottom brackets in mind, but it applies to adjustables just as well.

Let me know if any of this doesn't make sense and I'll try to explain further.

Also, you should be careful interchanging JIS and ISO spindles/cranks. If you use JIS cranks on ISO spindles, you could tighten too far and expand the taper so that the tightening bolt bottoms out on the spindle.

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Permalink Reply by Gecko on March 12, 2010 at 7:25am

You're welcome, glad I could help!

mfa cycle factory said:

Makes sense and similar to the data SB has on his site.. thanks for this.....It will come in handy.

I very rarely interchange bottom brackets, even though its a legal method as far as functionality goes. I do make sure that there is at least 1/8th of an inch thread sitting inside of the crank square so that the
bottom bracket nut will tighten against the crank and not against itself.

again, thanks for the data....it will come in handy.....

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